Preheat the oven to 350°F (175°C). Grease and flour a bundt pan.
In a mixing bowl, whisk together flour, baking powder, baking soda, cinnamon, and salt. Set aside.
In another bowl, cream together granulated sugar, brown sugar, and softened butter until light and fluffy.
Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Fold in the diced apples and nuts (if using).
Pour the batter into the prepared bundt pan and smooth the top.
Bake for 50-60 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then invert it onto a wire rack to cool completely.
For the glaze, mix powdered sugar and milk until smooth, then drizzle over the cooled cake.